1. Field of the Invention
This invention relates to engines using combined dual fuels and more particularly to a control system for mixing such fuels in a proper proportion.
2. Description of the Related Art
Gaseous fuel such as liquefied petroleum gas(LPG) and compressed natural gas (CNG) have long been recognized as fuels for motor vehicles. However, there are some disadvantages to each of these fuels. Natural gas and LPG while somewhat cheaper than gasoline and having lower emissions has a much lower energy density than gasoline and therefore requires much larger tanks to carry sufficient fuel. Further, there are a limited number of natural gas refueling stations. To combine the advantages of gaseous fuel with those of gasoline, fuel systems combining these fuels have been developed. Such a system is described in U.S. Pat. No. 4,641,625 issued Feb. 10, 1987 to Smith. In the system of this patent, the gaseous fuel flow rate is controlled by a microprocessor which controls such rate in response to engine speed and throttle position. Further, in Smith, the fuel pump is controlled to control the liquid fuel flow rate. The use of a microprocessor in Smith for controlling the gaseous fuel flow rate is a somewhat more complicated design than the simple mechanical control of the present invention. Further, the feeding of liquid fuel to the engine can be more effectively controlled by controlling the injection rate and duration by a simple processor, as in the present invention.